This invention relates to a centrifugal clutch.
A centrifugal clutch is composed of driving members, which are connected to driving means, and a driven member. The driving members consist, for example, of a clutch boss member and a plurality of clutch shoes mounted on the clutch boss member in such a manner as to be radially movable. The latter consists, for example, of a clutch drum arranged concentrically with respect to the clutch boss member. In such a centrifugal clutch, centrifugal force generated through rotation of the clutch boss member causes the clutch shoes to move outwardly in the radial direction. As a result, the clutch shoes are friction-engaged with the inner peripheral surface of the clutch drum, thereby transmitting the driving force from the clutch boss member to the clutch drum. Generally speaking, the clutch boss member and the clutch shoes of such a centrifugal clutch, both made of a metal such as sintered alloy, are separately manufactured as individual parts. Further, the surface of each clutch shoe which is friction-engaged with the inner surface of the clutch drum is equipped with an appropriate lining member. Such a construction inevitably involves a large number of parts. In addition, it takes much time and cost to manufacture and assembly them. Furthermore, a centrifugal clutch thus manufactured is rather heavy.
In order to eliminate the above problems, there has been proposed a centrifugal clutch construction that transmits a relatively low torque in which the clutch boss member and the clutch shoes are integrally formed using a plastic material. However, this proposed construction has a rather small specific gravity, so that it must having a considerably large size to be able to transmit torque satisfactorily. Furthermore, the heat generated between the clutch shoes and the clutch drum causes, in particular, the outer peripheral portions of the clutch shoes to melt and be deformed. In addition, since the clutch shoes and the clutch boss member do not conduct heat satisfactorily, their temperature rises, resulting in a considerable deterioration of operational force and strength. This also involves changes in clutch-in revolution. Because of these problems, this proposed construction has not yet been put into practical use.
Furthermore, a centrifugal clutch is a device of which considerable strength and accuracy are required. Accordingly, conventional centrifugal clutches of the type described above need the insertion of relatively hard reinforcing members of a metal or non-metal material in the section where the clutch boss member is mounted in order to secure fitting accuracy of the clutch and reinforce the clutch boss member which is fixed to a driving shaft. Accordingly, even when the clutch boss member and the clutch shoes are integrally manufactured using a plastic material, the steps of manufacturing and inserting the above-mentioned reinforcing members cannot be avoided, so that this proposed construction does not lead to reduced manufacturing costs. In addition, because of the necessity of providing reinforcing members, this conventional centrifugal clutch cannot be employed in a machine which does not easily allow the operation of inserting such reinforcing members during its manufacture.